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Chapter 27

Chapter 27. Human Genetics. The Role of Chromosomes. Chromosome Numbers in Living Things Each human sperm or egg has 23 chromosomes. Each human body cell has 23 pairs of chromosomes. Different organisms have different numbers of chromosomes. Human Cells. 23 Chromosomes. Sex Cells.

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Chapter 27

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  1. Chapter 27 Human Genetics

  2. The Role of Chromosomes Chromosome Numbers in Living Things • Each human sperm or egg has 23 chromosomes. • Each human body cell has 23 pairs of chromosomes. • Different organisms have different numbers of chromosomes.

  3. Human Cells 23 Chromosomes Sex Cells Chromosomes not paired 46 Chromosomes Body Cells Chromosomes arranged in 23 pairs

  4. Section 1 The Role of Chromosomes Chapter 27 Detecting Genetic Disease • Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring. • Amniocentesis is a way of looking at the chromosomes of a fetus.

  5. Section 1 The Role of Chromosomes Chapter 27 • Doctors can also take a small piece of the placenta to obtain a sample of chromosomes. • The chromosomes are counted and studied to see whether parts are missing. • Karyotypes are charts where chromosomes are organized in pairs.

  6. Section 1 The Role of Chromosomes Chapter 27 Sex – A Genetic Trait • Sex Chromosomes and Autosomes • Sex chromosomes contain genes that determine an organism’s sex (gender). • The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes.

  7. Section 1 The Role of Chromosomes Chapter 27 Sex – A Genetic Trait, continued • Sex Determination • In mammals, an individual carrying two X chromosomes is female. • An individual carrying an X and a Y chromosome is male.

  8. Section 1 The Role of Chromosomes Chapter 27 Karyotypes: Male and Female

  9. Section 1 The Role of Chromosomes Chapter 27 What are your chances of having male or female offspring? X X X XX X X Body Cell Eggs X XY Y Y Sperm Body Cell 1female:1male

  10. Section 1 The Role of Chromosomes Chapter 27 Male or Female? Who determines the sex of the offspring? • The Father, because he donates the Y chromosome.

  11. Section 2 Human Traits Chapter 27 Survey on Human Traits Attached earlobes is a Recessive trait. Detached earlobes is a Dominant trait.

  12. Section 2 Human Traits Chapter 27 Survey on Human traits Being able to roll your Tongue is a dominant Trait. Not being able to roll your Tongue is a recessive trait.

  13. Section 2 Human Traits Chapter 27 Survey on Human traits

  14. Section 2 Human Traits Chapter 27 Survey on Human traits

  15. Section 2 Human Traits Chapter 27 Incomplete Dominance Some traits are neither totally dominant nor totally recessive. Incomplete dominance is when neither gene is totally dominant to the other.

  16. Section 2 Human Traits Chapter 27 Incomplete Dominance Snapdragons

  17. Section 2 Human Traits Chapter 27 Incomplete Dominance • Sickle Cell Anemia • R = Round blood cells • R’ = Sickle Cells R R’ R R’

  18. Section 2 Human Traits Chapter 27 Blood Types in Humans • There are four blood types in humans – A, B, AB and O. • A and B are dominant to O.

  19. Section 2 Human Traits Chapter 27 Genes on the X Chromosome • Sex-Linked Genes and Traits • Genes found on the X chromosome are X-linked genes. • A sex-linked trait is a trait whose gene is located on a sex chromosome. • Because males have only one X chromosome, a male who carries a recessive gene on the X chromosome will exhibit the sex-linked trait.

  20. Section 2 Human Traits Chapter 27 Genes on the X Chromosome • Color blindness is a problem in which red or green look like shades of gray or other colors. • The gene is carried on the X chromosome and is a recessive trait. XC Xc XC Y

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